1. Field of the Invention
The present invention relates to a vehicle automatic transmission, and more particularly to a vehicle automatic transmission having a hydraulic torque converter and a multiple-stage transmission gear mechanism connected with the torque converter. More specifically, the present invention pertains to a control of a vehicle automatic transmission of the aforementioned type.
2. Description of the Prior Art
In a vehicle having an automatic transmission comprised of a torque converter and a multiple-stage transmission gear mechanism, a shift lever is provided for selecting one of an N-range (neutral), D-range, 2-range, 1-range, R-range (reverse) and P-position (parking). It has been experienced in this type of vehicle that if the vehicle is kept stationary with the shift lever positioned in a running range such as the D-range or the 2-range, the engine idle vibrations are transmitted through the transmission to the vehicle body disturbing the riding comfort. In order to solve the problem, the transmission gear mechanism may be brought into the neutral position even when the shift lever is in the running range. It should however be noted that this solution is not satisfactory because a shifting shock is produced when the shift lever is moved from the N-range to the running range, such as the D-range, 2-range and 1-range. This type of shifting shock is sometimes referred to as the "N-D shock" and caused by the fact that a power transmitting gear train is established in the transmission gear mechanism through engagements of appropriate friction members when the shift lever is actuated, to make it possible to transmit the engine output power through the gear mechanism to the wheels of the vehicle. This problem can be solved by having a higher gear stage such as a third or fourth gear stage to engage, in lieu of making the gear mechanism neutral, so that the driving torque transmitted to the driving wheels can be made smaller and the engine idle vibration transmitted to the vehicle body can therefore be reduced. Japanese patent application 54-131972 filed on Oct. 12, 1979, and disclosed for public inspection on May 20, 1981, under the disclosure number 56-57524 proposes, under a condition wherein the vehicle is stopped with the shift lever in a running range, to hold the gear mechanism in the first stage for a predetermined time and then automatically shift up to a higher stage, such as the third or fourth gear stage, after the predetermined time. With the control as proposed by the Japanese patent application, it is possible to start the vehicle smoothly utilizing the creep phenomenon of the torque converter within the predetermined time after a vehicle stop. It is also possible to reduce the engine idle vibrations transmitted to the vehicle body when the vehicle is kept in the stopped condition beyond the predetermined time.
It should, however, be noted that the control as proposed by the Japanese patent application is not satisfactory because the transmission of the engine idle vibrations cannot be suppressed during the predetermined time. Further, it becomes impossible to utilize the creep phenomenon of the torque converter for a smooth start of the vehicle after the vehicle has been stopped beyond the predetermined time.